The present invention relates generally to an optical circulator for fiber optic communication systems. More particularly, this invention relates to a loop optical circulator.
An optical circulator is a device employed to transfer a light beam in a sequential order from one port to another. A circulator has at least three optical ports. These ports can be accessed in such order that when a light beam is caused to enter into an optical port, this light-beam after passing through the circulator to exit from a next optical port. For example, a first optical beam enters the circulator through the first port of an optical circulator exits from the second port; an optical beam enters the circulator from a second port exits from the third port. An optical circulator is an important passive device that has a non-reciprocal function. As the conventional circulators available in the marketplace are mostly non-circular in nature, there is a need in the art to provide a close loop circulator for more flexible applications, particularly in bi-directional optical signal transmissions as will be further described below.
Therefore, a need still exists in the art of manufacturing and designing the fiber optic circulator to provide improved close-loop circulator configuration. Specifically, novel and improved circulator configurations enable a circulator having four optical ports that is capable to function as a close loop optical circulator for bi-directional optical signal transmission is highly desirable.
It is therefore an object of the present invention to provide an improved design and configuration for manufacturing a fiber optic circulator to achieve loop signal transmission and has compact volume and low production cost such that the aforementioned difficulties and limitations in the prior art can be overcome.
Specifically, it is an object of the present invention to provide a circulator implemented with improved configuration by employing polarization-dependent vertical-displacement means for vertically shifting the optical paths for particularly polarized beams to achieve a close-loop circulator. The flexibility and capacities of optical signal transmissions are improved with close-loop circulator available for more complete bi-directional signal transmissions.
Another object of the present invention is to provide a circulator with improved configuration by taking advantage of the non-reciprocal characteristic of Faraday rotator coupled with the polarization-dependent beam-displacement function of a walk-off crystal and polarization beam splitter. Symmetrically transmissions of forward and backward projected beams from different ports are therefore achieved.
Briefly, in a preferred embodiment, the present invention includes an optical circulator. The optical circulator includes a four-port optical circulator. The circulator includes a first, a second, a third and a fourth optical ports for receiving optical beam therein. The circulator further includes a plurality of optical components for guiding a beam received from the first port to project from the second port, for guiding a beam received from the second port to project from the third port. The optical components are used for guiding a beam received from the third port to project from the fourth port, and for guiding a beam received from the fourth port to project from the first port. In a preferred embodiment, the plurality of optical components further include a walk-off crystal for generating a vertical optical path displacement for a vertical polarized optical beam and for passing a horizontally polarized optical beam therethrough maintaining a same optical path.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.